Cannot flash/debug STM32WL55JC

Hello,

When trying to flash a Nucleo WL55JC1 (stm32wl55jci7u) using the command pyocd flash --target STM32WL55JCIx --frequency 1800000 -O connect_mode=under-reset mbed-os-example-blinky.bin I receive transfer errors. I am running the latest ST Link firmware (3.10.3) and have installed the Keil.STM32WLxx_DFP.1.1.0-small.pack CMSIS pack for this chip using pyocd pack install but it is the same if I use the one bundled with Mbed Studio or one downloaded directly from CMSIS.

On first attempt I get:

0000574 E Transfer error while reading AHB-AP#1 ROM table: Memory transfer fault (read) @ 0xf0000fd0-0xf000102f [ap]
Traceback (most recent call last):
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 797, in find_components
    cmpid.read_id_registers()
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/rom_table.py", line 124, in read_id_registers
    regs = self.ap.read_memory_block32(self.top_address + self.IDR_READ_START, self.IDR_READ_COUNT)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/utility/concurrency.py", line 29, in _locking
    return func(self, *args, **kwargs)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 1216, in _accelerated_read_memory_block32
    return self._accelerated_memory_interface.read_memory_block32(addr, size,
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/probe/stlink_probe.py", line 301, in read_memory_block32
    return conversion.byte_list_to_u32le_list(self._link.read_mem32(addr, size * 4, self._apsel, csw))
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/probe/stlink/stlink.py", line 473, in read_mem32
    return self._read_mem(addr, size, Commands.JTAG_READMEM_32BIT, self.MAXIMUM_TRANSFER_SIZE, apsel, csw)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/probe/stlink/stlink.py", line 423, in _read_mem
    raise exc
pyocd.core.exceptions.TransferFaultError: Memory transfer fault (read) @ 0xf0000fd0-0xf000102f
0000591 I Loading /home/rikki/Mbed Programs/mbed-os-example-blinky-baremetal/BUILD/NUCLEO_WL55JC/ARMC6/mbed-os-example-blinky-baremetal.bin [load_cmd]
[==================================================] 100%
0001317 I Erased chip, programmed 23552 bytes (23 pages), skipped 0 bytes (0 pages) at 31.69 kB/s [loader]

and on subsequent attempts I get:

0000632 E Error reading AP#1 IDR: Memory transfer fault (STLink error (17): AP fault) [discovery]
Traceback (most recent call last):
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/discovery.py", line 162, in _create_1_ap
    ap = AccessPort.create(self.dp, ap_address)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 367, in create
    ap.init()
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/utility/concurrency.py", line 29, in _locking
    return func(self, *args, **kwargs)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 1256, in init
    super().init()
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/utility/concurrency.py", line 29, in _locking
    return func(self, *args, **kwargs)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 778, in init
    _init_hprot()
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 746, in _init_hprot
    csw = AccessPort.read_reg(self, self._reg_offset + MEM_AP_CSW)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/utility/concurrency.py", line 29, in _locking
    return func(self, *args, **kwargs)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/ap.py", line 453, in read_reg
    return self.dp.read_ap(self.address.address + addr, now)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/coresight/dap.py", line 875, in read_ap
    result_cb = self.probe.read_ap(addr, now=False)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/probe/stlink_probe.py", line 207, in read_ap
    result = self._link.read_dap_register(apsel, addr & 0xffff)
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/probe/stlink/stlink.py", line 521, in read_dap_register
    self._check_status(response[:2])
  File "/home/rikki/.local/lib/python3.10/site-packages/pyocd/probe/stlink/stlink.py", line 363, in _check_status
    raise self._ERROR_CLASSES[status](error_message)
pyocd.core.exceptions.TransferFaultError: Memory transfer fault (STLink error (17): AP fault)
0000657 I Loading /home/rikki/Mbed Programs/mbed-os-example-blinky-baremetal/BUILD/NUCLEO_WL55JC/ARMC6/mbed-os-example-blinky-baremetal.bin [load_cmd]
[==================================================] 100%
0001769 I Erased 24576 bytes (12 sectors), programmed 23552 bytes (23 pages), skipped 0 bytes (0 pages) at 20.69 kB/s [loader]

Is this indicating that the pack is malformed? How do I fix this?

Reproduce the reported command with the Nucleo WL55JC1 and inspect the pyocd/coresight/ap.py, discovery.py, rom_table.py, and probe/stlink_probe.py paths named in the trace. Compare the first and subsequent AP transfer failures and verify that flashing and debugging complete without transfer faults.